The present invention relates generally to flow indicators for intravenous infusion devices.
Intravenous infusion devices are employed in both hospital and home environments. In all environments, it is essential to monitor continuity of flow, since discontinuity in flow can have extremely serious consequences for the health of a patient receiving an intravenous infusion.
In a hospital environment, intravenous infusion is either gravity or pump driven. Gravity driven devices typically include drip chambers which enable flow to be monitored by professional staff. Pump driven devices typically include various displays and alarms which indicate flow discontinuities.
In a home environment, there are known various electronic pumps as well as disposable mechanical devices such as elastomeric infusers and spring loaded mechanisms. Examples of such devices include the Infusor device marketed by Baxter Healthcare and the Paragon device marked by I-Flow. Devices of this type often operate at extremely low flow rates as slow as 0.5 ml/hr. Flow indications are provided either by volume gradations or a dipstick-like device, however, due to the low flow rates, resulting in small changes in volume, it may take a long time, up to 15-30 minutes or more, to observe a volume change.
The lack of a reliable and quick way to ascertain flow continuity is an important shortcoming of currently available infusion devices for home use and is a known cause of anxiety in home patients.
Published PCT application WO 96/34651 describes a highly complex mechanical construction for indicating flow in a disposable infusion device at specific rates over extended periods of time.
Drip chambers are conventionally employed to detect infusion flow. They are not normally suitable for use in ambulatory infusion because when they are oriented horizontally or upside-down they may release trapped air into the infusion line which both endangers the patient and renders the drip chamber inoperable, since it fills with liquid.
Applicant/Assignee""s copending Published PCT application WO 96/29104 describes a drip chamber which does not lose air due to the provision of a hydrophilic membrane positioned at the outlet. The membrane allows free passage of liquid therethrough but prevents air passage therethrough at all pressures below the bubble point of the membrane.
Although it has an important advantage in preventing air intrusion into the infusion line, the drip chamber of application WO 96/29104 is nevertheless inoperable in an upside-down orientation because air comes into contact with the membrane and ceases flow.
The present invention seeks to provide a simple to use, inexpensive and efficient intravenous infusion flow indicator, which is capable of demonstrating flow at even the lowest infusion rates commonly used and which does not require observation time exceeding about 30 seconds.
There is thus provided in accordance with a preferred embodiment of the present invention an intravenous infusion flow indicator including a housing defining an infusion liquid inlet and an infusion liquid outlet, a hydrophilic membrane disposed in the housing and being operative, when wetted, for permitting liquid flow and preventing air flow therethrough to the liquid outlet, the housing defining at least one volume, whose size and configuration are selected relative to the pressure of the infusion liquid at the infusion liquid inlet such that irrespective of the orientation of the housing following priming, infusion liquid within the housing is always in wetting relationship with the membrane, thereby permitting continued infusion liquid flow therethrough.
In accordance with a preferred embodiment of the present invention, the housing defines first and second volumes communicating with each other, the first volume being greater than the second volume, the configuration and the sizes of the first and second volumes being selected such that when the housing is in an upright configuration, the second volume is generally filled with air such that drops falling therethrough can be readily viewed for monitoring.
In accordance with one embodiment of the invention, the membrane has generally disc shape, the first volume has a generally flat cylindrical configuration and the second volume has a generally cylindrical configuration which is narrower and taller than the first volume.
In accordance with another embodiment of the invention, the membrane has a generally ring shape, the first volume has a generally top hat shape including a narrow high portion and a broad flat portion adjacent the membrane and the second volume has a generally cylindrical configuration similar to that of the narrow high portion.
In accordance with a preferred embodiment of the present invention, the infusion liquid is supplied through a narrow diameter liquid inlet, providing small drops in relatively quick succession, thus enabling the observation of flow rates as low as 0.5 ml/hr. For example, an inlet tube of inner diameter of 0.2 mm may be employed.
Additionally in accordance with a preferred embodiment of the present invention the membrane has a generally ring shape, the first volume and second volumes have generally semi-ellipsoidal configurations and the second volume is generally cylindrical of larger size than the first volume.
Further in accordance with a preferred embodiment of the present invention the membrane has a generally ring shape, the first volume has a generally semi-ellipsoidal shape and a broad flat portion adjacent the membrane and the second volume has a generally semi-ellipsoidal configuration.
Additionally in accordance with a preferred embodiment of the present invention the housing comprises a first element and a second element, wherein the second element includes a shoulder portion, and a diameter of the first element is chosen so as to define a volume when the first element and the second element are sealingly joined together.
There is also provided in accordance with a preferred embodiment of the present invention a method for indicating an intravenous infusion flow including providing a housing defining an infusion liquid inlet and an infusion liquid outlet and a hydrophilic membrane disposed in the housing and being operative, when wetted, for permitting liquid flow and preventing air flow therethrough to the liquid outlet, the housing defining at least one volume, whose size and configuration are selected such that irrespective of the orientation of the housing following priming, infusion liquid within the housing is always in touching relationship with the membrane, thereby permitting continued infusion liquid flow therethrough; priming said membrane with infusion liquid for full wetting thereof, and supplying infusion liquid under controlled pressure via said housing and said membrane to a patient.
Further in accordance with a preferred embodiment of the present invention the housing defines first and second volumes communicating with each other, the first volume being greater than the second volume, the configuration and the sizes of the first and second volumes being selected such that when the housing is in an upright configuration, the second volume is generally filled with air such that drops falling therethrough can be readily viewed for monitoring.
Still further in accordance with a preferred embodiment of the present invention the membrane has a generally disc shape, the first volume has a generally flat cylindrical configuration and the second volume has a generally cylindrical configuration which is narrower and taller than the first volume.
Additionally in accordance with a preferred embodiment of the present invention the membrane has a generally ring shape, the first volume has a generally top hat shape including a narrow high portion and a broad flat portion adjacent the membrane and the second volume has a generally cylindrical configuration similar to that of the narrow high portion.
Moreover in accordance with a preferred embodiment of the present invention the infusion liquid is supplied to the liquid inlet via narrow diameter tubing, providing small drops in relatively quick succession, thus enabling the observation of flow rates as low as 0.5 ml/hr.